Circular weft knitting machines of the general type herein of interest are both old and well known in the art. The basic precepts determinative of the circular weft knitting operation extend back over 70 years and the intervening period has been characterized by a progression of generally relatively minor and essentially unitary component improvements, all to the general end of increasing machine speed and/or versatility but, in general, with little or no radical departures from fundamental structure or mode of operation.
While the machine variants employed in present day commercial operations are legion, most, if not all, of the commercially available circular weft knitting machines conventionally include a rotatably displaceable cylinder member having a multiplicity of longitudinal grooves on its outer surface, with each of said grooves containing and guiding a single frictionally restrained but reciprocally displaceable knitting needle member therein. Such needles are selectively displaced in relation to a yarn feed location to permit successive needle-yarn engagements and introduction of engaged yarn into the previously knit portions of the article being fabricated. Among the known needle member constructions, the most commonly employed is the so-called "latch" needle employing a pivotally mounted latch element at the hook bearing end of the needle element that is rotatably displaceable between a hook open and a hook closed position. Another variant, the so-called "compound" needle employs a separate and independently displaceable longitudinally reciprocable closing element in association with each needle element. Such compound needle construction has long offered marked advantages in both fabric quality and speed of fabric formation through diminution of stroke length and permitted positive closing element control; however such advantages have never attained substantial commercial fruition. Another known needle construction is the so-called "spring beard" needle which does not reciprocate longitudinally of the rotating knitting cylinder. A common field of use for such needles has been in the fabrication of sweatshirts and similar articles.
Individual needle reciprocation for the most commonly employed latch type needle within its respective path defining and confining groove on the periphery of the knitting cylinder has been most commonly initiated and effected through needle engagement with elevating cams with the latter in turn being operatively controlled through selectively shaped "selection jacks". In turn, each selection jack is vertically actuated by a jack cam induced displacement after radial displacement by a presser cam. An associated control selector, conventionally an extending pin on a rotating drum or the like adapted to engage the selector plate cams which in turn contact the selection jack, operates to associate or dissociate the selection jack from the jack cam. When the selection jack is displaced by the jack cam it elevates an extending cam butt on the needle into operative driving engagement with an adjacent cam track or the like. In such systems, the pin location settings of the control members and selection jack butt contour essentially constitute a mechanical program to selectively displace the needles, through intermediate displacement of their respective selection jacks, into operative engagement with an associated cam track and to thereby control both the nature and extent of reciprocable needle displacement and which, in turn, is at least partially determinative of workpiece configuration and patterning. In such mechanically programmed machines, the selection jacks are normally selectively contoured and such jacks, together with the mechanical programming device must be modified and/or replaced whenever a configuration or pattern change in a product being fabricated is involved. That is to say, while such conventional circular weft knitting machines may be mechanically programmed to produce a particular shape and/or pattern for a given product they must also be basically modified, a relatively time consuming and expensive manual procedure requiring highly skilled personnel, whenever the shape and/or pattern of the product is to be changed. One practical result of such required program modification is either excessive machine downtime or buildup of undesired inventory if units are permitted to continue operation after completion of a particular production order. In conjunction with the above, conventional machine structure has generally also operated to limit mechanical programming to a selection between "tucking" or "floating" or to a selection between "knitting" or "floating" at a given yarn feed location. Conventional mechanical constructions or heretofore electronically programmable machines do not provide for Jacquard selection among "knitting", "tucking" and "floating" operations at each yarn feed location.
Apart from the above noted time-consuming and expensive character of manual program modification, the conventional circular weft knitting machines are also highly and unduly dependent upon the immediate availability of such highly skilled personnel in order to maintain any appreciable continuity of operation. Among the continued set-up and maintenance operations required is the bending or "setting" of the needle elements necessary to maintain the requisite degree of frictional engagement thereof within the slots on the knitting cylinders to avoid inadvertent displacement thereof and the selective modification of parts including part reshaping and redefinition of frictionally engaged surfaces such as cam tracks and the like, to accommodate wear.
Over the more recent years and in an effort to increase machine versatility and accommodate greater fabric patterning complexities, attempts have been made to incorporate electromechanical needle selection and displacement control systems in circular weft knitting machines, such as by actuating selection jack displacement through tape controlled solenoids or the like. However, such improvements, at least to date, are ones of degree only and have not, because of practical considerations such as undue power consumption, slow speed of operation and lack of operational reliability, been commercially employed on any widespread basis.
Commercial circular weft knitting machines also conventionally employ a multiplicity of "sinker" members, each radially reciprocable relative to the knitting cylinder and in a path essentially normal to that of needle displacement, to cooperate with the yarn feed and with the individual needle members in effecting stitch draw and stitch hold-down operations. Such sinkers are conventionally mounted on either an internal sinker pot or on an external sinker bed plate rotatable with the rotatable knitting cylinder and are individually radially displaced relative thereto by a separate cam track. Conventionally, the initiation and extent of individual radial sinker displacement is selectively determined by the character of such cam track. Certain recent developments have been directed to incorporating a limited capability to independently move the sinker members in the vertical direction intermediate periods of radial displacement thereof in order to reduce yarn tension and barre. However such developments have had only limited commercial use at the present time, largely because of mechanical problems attendant thereto.
While circular weft knitting machines conventionally employed in fabric knitting employ only a single direction of knitting cylinder rotation, circular knitting machines conventionally employed in hosiery fabrication often incorporate means for effecting reversal of direction of knitting cylinder rotation. Such machines, however, have been capable of traversing only a single fixed distance in the reverse direction in accord with machine design. Such machines also employ two individually nonsymmetrical but essentially 180.degree. out-of-phase or reversed cam track contours, each adapted to accommodate only unidirectional needle element movement therewithin, to achieve stitch draw and latch clearing operations for such bidirectional knitting cylinder displacement. In such standard construction, not only are two individually nonsymmetrical cam tracks employed, but such cam tracks are necessarily "open" at the crossover or junction points, at which location the needle members are subject to undesired and/or uncontrolled displacement in the vertical direction. As noted above, needle displacement, in conventional circular knitting machines, is effected against the frictional forces normally restraining needle movement and such frictional forces are normally the only forces that operate to restrain undesired and unintentional needle movement as might occur at the open cam track crossover points or the like.
Conventional circular weft knitting machines are also generally characterized by a multiplicity of selectively positionable components that are determinative of the nature of the displacement paths taken by the yarn engaging elements in the knitting operation both in accord with the nature of track defining surfaces thereon and in accord with how such components are positioned relative to other machine components. Within this two variable environment, modification of both the contour of the control track surfaces and the positioning of the components is most usually manually effected for each yarn feed within each machine in accord with the visually observed nature of the product being fabricated. Such manual modification and positional adjustments are not only effected in accord with the desires of individual maintenance personnel but have the cumulative result that every machine is or rapidly becomes effectively unique in both its structure and in its operation with an accompanying cumulative lack of reliability of operation on a repetitive basis.
It is often desirable to incorporate, in circular weft knitting machines, the capability of forming a so-called "terry cloth" type of surface on all or on a portion of a knitted article, such as on the sole and/or heel portions of a sock to enhance both wearer comfort and durability. Such "terry cloth" surface is formed by incorporating into the fabric a multiplicity of extending yarn loops, conventionally termed "terry loops". In most circular weft knitting machines, the formation of such "terry loops" is conventionally effected through the use of sinkers with an elevated land which serves to divide the converging yarns during the stitch draw operation. Other circular weft knitting machines employ auxiliary yarn feed engaging elements known as terry "bits" or terry "instruments". In the latter type construction, the terry bits are conventionally mounted for individual radial displacement relative to the knitting cylinder and in a path normal to that of needle displacement within a terry dial in a suspended housing assembly disposed above and coaxial with the knitting cylinder. Such terry bits conventionally include a cam butt that is selectively engageable with one of two stationary cam tracks. When a terry bit cam butt is operatively engaged in one of such cam tracks, the terry bit is appropriately subject to radial displacement and cooperates with the reciprocating needles and the yarn feed mechanism to form the desired terry loops. In contradistinction thereto, when the terry bit cam butts are disposed in the other cam track, the terry bits will be positioned in a retracted location out of the path of needle displacement and yarn feed and are so rendered effectively inoperative.
As pointed out above, the development of circular weft knitting machines of the type herein of interest has been characterized by a progression of generally relatively minor and essentially unitary component improvements with little or no radical departures from fundamental structure or mode of operation. The economic pressures that have been attendant recent years have served however to accentuate the long recognized and continued need for circular weft knitting machines of significantly increased reliability and expanded versatility as to increased pattern and contour capabilities in general, a marked diminution in the dependence upon the highly skilled set-up and maintenance personnel who are of limited availability and for circular weft knitting machines of significantly increased speed of operation with consequent higher unit production rates as well as a diminution of the time required for machine changeover to accommodate either product or pattern changes. Unfortunately, however, commercially available circular weft knitting machines have not met such needs and are, at the present time, generally subject to one or more of the following disabilities, the net effect of which has effectively precluded the attainment of the desired objective of the provision of an improved circular knitting machine of significantly increased reliability, versatility, speed of operation and economy of production.
Among such long recognized disabilities are an inherent lack of reliability of machine operation; undue downtime required for machine modification to accommodate product or pattern change; undue dependence upon the unique abilities of individual maintenance personnel; cumulative modification of individual machine components in accord with exigencies dictated by visual product observation; limitation on stitch draw speed directly attributable to necessary usage of needle butt cam track slopes of 45.degree. or less in association with vertically fixed verges or sinkers; the inability of machines employing latch type needles to positively control latch element displacement independently of needle reciprocation; the lack of an effective control over stitch length; excessive length of required needle displacement; speed limitations inherent in mechanical needle selection and in the power usage and speed limitation attendant electromechanical needle selection and in the conventional employment of surface interrupted cam tracks controlling the nature and extent of needle displacement; the lack of effective means to assure uniform yarn feed; inability to control yarn tensions and the robbing back of yarn from immediately preceding knit operations and consequent product variation; the limitation of the number of permissible yarn feed stations within a 360.degree. circumference for a given knitting cylinder diameter; a basic lack of awareness of the status of the actual knitting operation in progress in comparison to desired programmed operation, except through visual observation of the product being fabricated; inability to selectively vary terry loop lengths; the inability to utilize a plurality of simultaneous yarn feeds and to produce uniform fabric from each feed; and the inability to symmetrically operate when the knitting cylinder is in a reciprocatory or bidirectional mode of operation.
The foregoing are but some of the generally characteristic, if not inherent, structural and operational limitations of the state of the art circular weft knitting machines. The subject invention, as hereinafter described and claimed, represents a radical departure from conventional technology in a number of the basic circular weft knitting machine operational steps and component subassemblies, the individual and combined effect of which is to provide a markedly improved and electronically preprogrammable circular weft knitting machine construction that incorporates novel methods of machine operation and component displacement to the end of providing commercially significant and readily realizable improvements in product contour and patterning versatility at significantly increased speeds, with improved operational reliability and attendant economies of operation that flow therefrom and from reduced dependence upon highly skilled maintenance and operating personnel.